In a methanol plant, a synthesis gas (for example, methanol) is produced from a feed stock (for example, natural gas). In a case of synthesizing methanol from natural gas, in general, a reformed gas which includes hydrogen and carbon monoxide is produced by steam-reforming natural gas, and methanol is synthesized from the gas.
In a case of synthesizing methanol or methanol-via gasoline from natural gas, natural gas and water (fresh water) are required as a feed stock. However, in such a methanol plant, there is a problem in that fresh water is very scarce in a desert area of the Middle East, North Africa, or the like, or an area such as the North Pole.
In a case of synthesizing methanol or methanol-via gasoline from natural gas, since fresh water is required, a technique of obtaining fresh water from seawater or brine by desalinated seawater or brine is known. In order to perform the desalination, PTL 1 discloses a production apparatus of fresh water from seawater or brine, in which evaporation (flash) is performed by heating seawater or brine and cooling is performed again, thereby obtaining fresh water.